Upper lower Eocene calcareous nannoplankton from the Las Pocitas core (Tepetate formation), Baja California Sur, Mexico

Abstract

Sixty species of calcareous nannoplankton from the Tepetate formation were recovered from a drill hole near Las Pocitas, Baja California Sur. In spite of its low abundance and erratic distribution throughout the sedimentary column, the great amount of reworked species, as well as the absence of traditional index fossils representing the standard tropical biozonation, the co-occurrence of Reticulofenestra dyctioda, Rhabdosphaera crebra, R. pinguis, Micrantholithus fl os, Pontosphaera pectinata and Lanternithus minutus situates the studied stratigraphic column at the Discoasteroides kuepperi CP12a Subzone of Okada and Bukry, dated between 49.5 and 49 Ma at the top of the upper lower Eocene.

The population structure as well as the lithological features of the sedimentary package, suggest a temperate open-sea deposit, which confi rms interpretations based on other marine fossils at arroyo Datilar, El Conejo, Salada, Colorado y Las Pocitas, where rocks of the lower middle Eocene Tepetate formation crop out.